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CVE-2026-64379
smb: client: mask server-provided mode to 07777 in modefromsid
Published 2026-07-25 (3 months ago) by the Linux kernel CNA. Subsystem fs/smb. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-64379 in every release this site tracks, and what each one means in practice. Every status below is the one the Debian Security Team publishes for this CVE. source
| Release | Status | Version | What this means |
|---|---|---|---|
| Debian 12bookworm | fixedDLA-4720-1 · 2026-08-05 · text | 6.1.180-1 | Update the kernel and reboot. DLA-4720-1 shipped the fix on 2026-08-05, in 6.1.180-1. A running kernel keeps the old code until the machine restarts. |
| Debian 13trixie | fixed | 6.12.96-1 | Update the kernel and reboot. Fixed in 6.12.96-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.1.4-1 | Update the kernel and reboot. Fixed in 7.1.4-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.4-1 | Update the kernel and reboot. Fixed in 7.1.4-1. A running kernel keeps the old code until the machine restarts. |
| Debian 12bookworm · linux-6.12 | fixedDLA-4724-1 · 2026-08-07 · text | 6.12.100-1~deb12u1 | Update the kernel and reboot. DLA-4724-1 shipped the fix on 2026-08-07, in 6.12.100-1~deb12u1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
When modefromsid is active, parse_dacl() applies the server-provided sub_auth[2] value from the NFS mode SID to cf_mode without masking to 07777. Apply the correct masking, same as in the read path.
Where it lives
The fix touches these files. If the subsystem is one you do not use, the practical exposure is lower, though the package is still the vulnerable one.
fs/smb/client/cifsacl.c
- What this is
- COMMON INTERNET FILE SYSTEM CLIENT (CIFS and SMB3)MAINTAINERS section matched on fs/smb/client/ · linux-cifs@vger.kernel.org · Supported
- Kernel module
- cifs
Check it on the machine
grep -wE 'CONFIG_CIFS|CONFIG_SMBFS' /boot/config-$(uname -r)Reads the booted kernel's own configuration, on the machine and nowhere else. =y is built in, =m is a module, and an is not set line means the code is not there.
lsmod | grep -w cifsPrints a line if that module is loaded right now, and nothing if it is not. One that is not loaded can still be loaded later by anything that needs it.
Show whether Debian builds this, per release
Debian builds this as a loadable module. Every release below compiles it as a module on every flavour, so whether the code is in the running kernel depends on whether that module is loaded.
- bookworm, trixie, forky, sid, bookworm · linux-6.12m
- m
- a loadable module on every flavour - check lsmod, can be blacklisted
- Build switches
- CONFIG_CIFS, CONFIG_SMBFS
- Reads as
- all on means the file is compiled; any one off means it is not.
From the configuration Debian publishes for every kernel flavour it builds. It covers only the architectures Debian ships a linux-config package for, and nothing about a kernel you built yourself. Debian's own status above stays authoritative about the source package.MAINTAINERS kbuild Makefiles Debian linux-config packages
Signals
- Published
- 2026-07-25 (3 months ago)source
- CVSS
- 7.1 high
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:Hsource recompute it - Attack vector
- network (AV:N)source
- EPSS
- 0.31%, higher than 22.2% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- fs/smb
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 5.4 | 5.10.261 | 5f6f2241034f |
| 5.4 | 5.15.212 | ee2216dbdf0c |
| 5.4 | 6.1.178 | f511807feee7 |
| 5.4 | 6.6.145 | 08c600b7e181 |
| 5.4 | 6.12.96 | b84e002e0df2 |
| 5.4 | 6.18.39 | c6c484a7d5bf |
| 5.4 | 7.1.4 | f80add1bfb34 |
| 5.4 | 7.2 | e3d9c7160d48 |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4724-1 | 2026-08-07 | bookworm 6.12.100-1~deb12u1 | tracker |
| DLA-4723-1 | 2026-08-07 | bullseye 6.1.180-1~deb11u1 | tracker |
| DLA-4720-1 | 2026-08-05 | bookworm 6.1.180-1 | tracker |
| DLA-4717-1 | 2026-08-05 | bullseye 5.10.262-1 | tracker |
Why the CNA scored it this way
Quoted from the kernel CNA's own scoring file, word for word. A highlighted metric carries the most severe value CVSS v3.1 defines for it, which is what pushes the score up. source
- AV:NAttack vector, network
- A malicious or compromised SMB server can supply the crafted NFS mode SID through a network-delivered QUERY_INFO security descriptor.
- AC:LAttack complexity, low
- With modefromsid enabled, the server directly controls sub_auth[2], and the invalid inode-type bits are applied deterministically without a race or memory-layout dependency.
- PR:NPrivileges required, none
- The attacker acting as the SMB server needs no privileges on the client; client authentication to the share is a victim-side condition rather than an attacker privilege.
- UI:RUser interaction, required
- A victim administrator or service must mount the SMB share with modefromsid, or subsequently access a crafted object on an existing mount.
- S:UScope, unchanged
- The corrupted mode and resulting VFS behavior remain within the Linux kernel's existing security authority and do not cross a VM, IOMMU, or sandbox boundary.
- C:NConfidentiality impact, none
- The flaw only injects bits into the 16-bit mode field and provides no out-of-bounds read, memory disclosure, or direct mechanism for returning client data to the attacker.
- I:LIntegrity impact, low
- The attacker can alter S_IFMT bits in cf_mode and thereby change the inode's perceived type and selected VFS operations, but this is a constrained metadata modification rather than an arbitrary write or control-flow primitive.
- A:HAvailability impact, high
- Forging the root or widespread inode types can prevent the share from mounting or render its objects unusable; for CIFS-root or critical SMB-backed deployments this can cause complete service availability loss.